The Amino Acids
(For each amino acid, both the three-letter and single-letter codes are given. CLICK the NAME to see the structural formula)
Alanine | Ala | A | hydrophobic
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Arginine | Arg | R | free amino group makes it basic and hydrophilic
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Asparagine | Asn | N | carbohydrate can be covalently linked ("N-linked) to its -NH
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Aspartic acid | Asp | D | free carboxyl group makes it acidic and hydrophilic
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Cysteine | Cys | C | oxidation of their sulfhydryl (-SH) groups link 2 Cys (S-S)
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Glutamic acid | Gly | E | free carboxyl group makes it acidic and hydrophilic
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Glutamine | Gln | Q | moderately hydrophilic
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Glycine | Gly | G | so small it is amphiphilic (can exist in any surroundings)
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Histidine | His | H | basic and hydrophilic
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Isoleucine | Ile | I | hydrophobic
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Leucine | Leu | L | hydrophobic
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Lysine | Lys | K | strongly basic and hydrophilic
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Methionine | Met | M | hydrophobic
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Phenylalanine | Phe | F | very hydrophobic
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Proline | Pro | P | causes kinks in the chain
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Serine | Ser | S | carbohydrate can be covalently linked ("O-linked") to its -OH
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Threonine | Thr | T | carbohydrate can be covalently linked ("O-linked") to its -OH
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Tryptophan | Trp | W | scarce in most plant proteins
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Tyrosine | Tyr | Y | -OH group makes it moderately hydrophilic
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Valine | Val | V | hydrophobic
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Humans must include adequate amounts of 9 amino acids in their diet. These "essential" amino acids cannot be synthesized from other precursors. However, cysteine can partially meet the need for methionine (they both contain sulfur), and tyrosine can partially substitute for phenylalanine.